Evolution of fault-induced salt precipitation due to convection of CO2 and brine along fault during CO2 storage in multilayered saline aquifer-caprock

Abstract

Till now, salt precipitation occurring in fault zone, named fault-induced salt precipitation, has not been reported for CO2 storage, although mineral precipitation has been reported occurring in Little Grand Wash Fault zone due to co-leakage of CO2 and water. Salt precipitation in fault zone can play critical roles to prevent CO2 leakage along fault, because the activated fault can be sealed by salt precipitation. In view of this, it would be investigated whether the salt precipitation can occur in fault and concluded for the evolution of fault-induced salt precipitation, especially considering convection of CO2 and brine along fault during CO2 storage in multilayered saline aquifer-caprock. In detail, the theoretical model was established to solve the solid saturation based on mass and energy conservation equations. By simplifying the discretized mass conservation equation, it could be found that salt precipitation was controlled by brine migration rate. Then, the physical model was proposed considering the convection of CO2 and brine along the fault, formed by CO2 migrating upwards and brine migrating downwards along fault. Furthermore, the numerical model was established to validate salt precipitation occurring in fault zone. The numerical results showed that: (i) the convection of CO2 migrating upwards and brine migrating downwards could be observed from velocity vectors of fluid migration; (ii) slow migration of brine could be found by comparing migration rates of CO2 and brine; (iii) salt precipitation indeed occurred in fault zone. By the numerical results, the evolution of salt precipitation was divided into three stages, namely, Stage I: convection of CO2 and brine; Stage II: slow migration of brine; Stage III: salt precipitation occurring. Finally, the parametric analyses were performed to investigate the effects of different parameters on salt precipitation. Results indicated that increasing in the injection rate and the fault height but decreasing in the injection time interval, the fault dip angle and the distance between fault and injection well were more beneficial for the salt precipitation in fault. The findings of this study can help for better understanding of the phenomenon of salt precipitation occurring in fault.